1. Field of the Invention
The present invention relates to an image processing method and apparatus like those employed in, for example, a laser beam printer and a light emitting diode (LED) printer, where an image is printed on a paper by way of arranging small pixels on a page in a particular arrangement with an associated resolution. More particularly, the present invention relates to image processing methods and apparatuses that employ image data correcting features that enhance the quality of a reproduced image that more closely resembles an original image.
2. Discussion of the Background
There have been laser beam printers, LED printers and other image processing devices that correct image data. These printers (or more generally apparatuses) write an image by laser beam or LED according to an inputted image data, and make a reproduction of the image by arranging small pixels on a paper or other image holding member. Among other things, these printers have to perform a function of converting multilevel signals to binary signals and, perform gray-scale image processing.
In these printers, an inputted image data is corrected by way of converting the multilevel signals to binary signals and performing gray-scale image processing on the binary signals and writing a resulting pattern of dots on the paper. Because an inputted image data is formatted as a multilevel signal, but printers can write only binary images (i.e., xe2x80x9cblackxe2x80x9d and xe2x80x9cwhitexe2x80x9d), the conversion process is employed.
In these conventional printers, the process of the converting multilevel signals to binary signals and performing gray-scale image processing is changed according to the kind of the inputted image, for example, a text image and graphics image. In some of these printers, an operator selects the process manually according to the kind of the inputted image, as perceived by the operator.
For a text image, the printers carry out a process of preventing jagged lines from being printed when the original image was a slanted line. FIG. 5 shows how the text image may be corrected where FIG. 5 is an enlarged view of an edge of a reproduced slanting line, and (A) is a diagram of before correcting and (B) is a diagram of after correcting. The pixels xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d in FIG. 5A are reduced in size to the corresponding pixels xe2x80x9caxe2x80x2xe2x80x9d and xe2x80x9cbxe2x80x2xe2x80x9d in diagram (B). Also, the pixels c, d, and e are added as part of the correcting process. By this correcting, the jagged edge on slanting line becomes smooth or reasonably smooth when viewed by a reader.
FIG. 6 is an enlarged view of a dot, which consists of several pixels and is used in a graphics image. The graphics image is made of many .dots by employing a dithering process, error diffusion and so on. A light and shade (density, gray-scale) of the graphic image is determined by the size of the dots. FIG. 6(A) is a diagram of before correcting and FIG. 6(B) is a diagram of the dot after correcting. In FIG. 6, the pixels xe2x80x9cxxe2x80x9d are reduced as xe2x80x9cxxe2x80x2xe2x80x9d and the pixels xe2x80x9cyxe2x80x9d are added to the existing dots as was done previously in FIG. 5B. Consequently, the jaggedness of the dot""s edge is reduced (i.e., a periphery of the corrected dot appears to be smooth, relative to the dot in FIG. 6A). However, the size of dot is changed after the correcting. Therefore, after the correcting, the light and shade of the image is not correct because the size of dot is changed.
In the previously discussed conventional printer, correcting is not executed for the image graphic, because this, changing of the light and shade of the image is undesired. For the same reason, the correcting is not executed for mixed text-and-graphics images.
As determined by the present inventor, an effective amount of correcting is dependent on the subject matter contained in the image. For example, when the slope of a slanting line is big, an intense amount of correcting is needed because the jaggedness of the slanting line is quite conspicuous. On the other hand, when the slope of a slanting line is small, an intense amount of correcting is not needed because the jaggedness of the slanting line is somewhat inconspicuous.
Accordingly, an object of the present invention is to provide a novel image processing method and apparatus with correcting image data features which obviates the above-mentioned problems.
Another object is to provide an image processing apparatus with correcting image data features that executes the correcting process suitably for each kind of image.
A further object of the present invention is to provide an image processing apparatus with correcting image data features that correct images with mixed text-and-graphics.
To achieve the above-mentioned and other objects, there is provided an image forming method and apparatus that includes a correcting image data mechanism having an input for inputting image data, a detector for detecting a shape of an edge of the image data from the input, a correcting mechanism for correcting image data from the input according to said shape of the edge of an image data from the detector and an output for outputting image data from the correcting mechanism.
There is also provided an image forming apparatus that includes an input unit for inputting image data, a detector for detecting a slope of an edge of the image data from the input unit, a comparing circuit for comparing the slope of an edge of an image data from the detector with a preset slope data, a correcting circuit for correcting image data from the input unit according to the result of the comparing operation performed by the comparing circuit and an output unit that outputs the corrected image data from the correcting circuit.